Such an accumulation device is already known to the expert. One such is described for example in document FR 2 524 436 and comprises a first linear conveyor belt configured to transfer items in a first direction, a second linear conveyor belt parallel to the first conveyor belt configured to transfer the items in a second reverse direction relative to the first and a third conveyor belt forming a semi-circle configured to transfer the items from the first conveyor belt to the second conveyor belt. The accumulation device also comprises translation means configured to translate the third conveyor belt relative to the first and second conveyor belt in the first direction or inversely in the second direction. This third conveyor belt is offset upwards relative to the first and second conveyor belts. Also, two ramps are arranged at the level of the two ends of the third conveyor belt and attached to the latter such that the translation of the third conveyor belt at the same time enables displacement of the ramps which slide vis-à-vis the first and the second conveyor belts to modulate the length of the accumulation device. These ramps enable products to rise from the first conveyor belt to the third conveyor belt and inversely enable products to descend from the third conveyor belt to the second conveyor belt. These ramps are constituted by a tab on which the products slide as they rise or descend under the effect of the thrust exerted by the products placed upstream and moving in the conveying direction on the conveyor belts. It is understood that the ramps slide on the first and the second conveyor belts at the same time as they move to the third conveyor belt, which can cause premature degradation of said first and second conveyor belts. Also, the design of the accumulation device according to this document FR 2 524 436 is particularly adapted for products having a low mass, such as biscuits. It is understood that if the mass of the products is much greater for example for bottles, such a ramp design can cause difficulties for transferring products from the first conveyor belt to the third conveyor belt and inversely from the third conveyor belt to the second conveyor belt, since said transfer is made by sliding on the tabs and therefore requires greater thrust of those products placed upstream, which can optionally slide on the first conveyor belt, or even tip over. Similarly, as products move from the first conveyor belt on the tab of the ramp, it is understandable that it can be difficult for products to surmount the edge of said tab, and this may cause the products to tip over.
Document JP 59 053315 also describes an accumulation device which comprises a ramp system associated with a semi-circular conveyor with rollers of gravity type having a descending slope whereof the input is elevated relative to the output. In this device, the conveyed items are pulled up by the ramp system from a first belt then descend under gravity to the second belt by travelling on the semi-circular conveyor with rollers from its input to its output located under the first end. Such a device does not convey series of products which have to stay in line relative to each other.